The present invention relates to a lithography method and a method for producing a wiring board, and more particularly relates to a method of producing a laminate having a circuit pattern built up on a substrate through an insulating photosensitive resin layer without generating any voids or bubbles in the insulating layer (photosensitive resin layer).
For example, in the method of producing a built-up laminate, the most important technical challenge is to prevent voids from being created during the formation of an insulating layer. The voids created in the insulating layer are classified into following three types:
1. voids created by bubbles contained in resin during the coating process;
2. voids created in the insulating layer by shadows of contaminant matter adhering to the pattern mask (glass) and the exposure equipment during the exposing process; and
3. voids created by shadows of contaminant matter adhering to the surface of the photosensitive resin during the exposing process.
Of the above three types of voids, the voids created by bubbles entered in the resin during the coating process is found to be negligibly small, so that no troubles such as short circuit or shortage of withstand voltage erupt. The voids created by shadows of contaminant matter adhering to the pattern mask and the like can be removed by being exposed to light twice. In the meanwhile, in order to prevent the creation of voids, contaminant matter adhering to the surface of photosensitive resin has been so far removed by using a roller coated with adhesive agent in such a way to attach the contaminant matter to the adhesive agent of the roller. It has been considered that the creation of voids can be effectively prevented in this way. However, close inspection reveals that voids are created on the surface of photosensitive resin layer, because the contaminant matter is not completely removed from the surface by the adhesive roller. Thus, some of the contaminant matter left on the surface causes the creation of voids.
Next, the cause of voids created in the photosensitive resin layer by contaminant matter will be explained below. As shown in FIG. 14(a), wirings 2 with a predetermined shape are formed on the insulating substrate 1, and a photosensitive resin layer 3 is formed on the substrate 1 and the wirings 2. A photomask 5, on which a shielding pattern is formed, is positioned as shown in FIG. 14(b), and then the photosensitive resin layer 3 is exposed to light so as to form a via hole 4 in a predetermined position of the photosensitive resin layer 3 as shown in FIG. 14(c). At this time, if contaminant matter 6 is on the surface of the photosensitive resin layer 3, it functions as a part of the shielding pattern, so that the photosensitive resin layer behind the contaminant matter 6 is not exposed to light. After performing several steps in a general manner, the developing step is carried out as shown in FIG. 14(c). Generally, in the developing step, the photosensitive resin layer 3 is overdeveloped to form the via hole 4 and the like. During this developing step, the contaminant matter 6 comes off from the photosensitive resin layer, and the part of the photosensitive resin layer 3, which is behind the contaminant matter 6 during the light exposure, is developed. Thus, a void 7 is formed on the photosensitive resin layer 3.
When the void 7 is created, the following problem arises. In order to produce a wiring board, the surface of the photosensitive resin layer 3 is removed by being ground as shown in FIG. 15(a), and then a conductive layer 8 is formed on the photosensitive resin layer 3 as shown in FIG. 15(b). Thereafter, as shown in FIG. 15(c), an upper wiring 9 is formed by developing the conductive layer 8 in a general manner, and thus the wiring board is produced. In producing the wiring board, when the upper wiring 9 is overlapped with the void 7 of the photosensitive resin layer 3, short circuit occurs if the upper wiring 9 on the bottom of the void 7 is brought into contact with the lower wiring 2, or a sharp reduction of withstand voltage occurs if the spacing between the two wirings 9 and 2 is narrow.
An object of the present invention is to prevent voids and bubbles from being created in the photosensitive resin layer by contaminant matter adhering to the photosensitive resin layer.
Another object of the present invention is to provide a method for producing a wiring board, whereby the creation of voids and bubbles on the photosensitive resin layer can be prevented and short circuit between wirings and reduction in withstand voltage can be prevented.